This invention relates generally to electrical circuit breakers and more particularly to such interrupters used as aircraft circuit breakers.
It is conventional for aircraft circuit breakers to have an overload responsive member such as a current carrying bimetal, typically called a bimetal trip arm, which has a portion which deflects with changes in temperature to move a slidably mounted connecting plate which is adapted to engage and displace a trip arm. One part of a latch mechanism is movable with the trip arm and upon occurrence of an overload the one part of the latch mechanism is separated from a catch portion which allows a collapsible linkage mechanism to move a movable contact into an open contacts position. Such a device is shown, by way of example, in U.S. Pat. Nos. 4,827,233 and 4,837,545, assigned to the assignee of the present invention, the disclosure of which is included a herein by this reference. Typically a high localized contact force exists between the interengaging surfaces of the latch and its catch. Such surfaces are manufactured so that they are extremely smooth and wear resistant, using expensive materials thereby increasing component costs. Although such devices are effective, the friction of the latching mechanism tends to change over time introducing variability and can eventually change the calibration of the circuit breaker. Additionally, such devices require a relatively large number of components, particularly in multiphase breakers where several contact, linkage and latch mechanisms are ganged together.
It is an object of the invention to provide circuit breaker free of the prior art limitations noted above. Another object of the invention is the provision of an electrical circuit breaker which performs the same functions as conventional aircraft circuit breakers yet has no latch mechanism with concomitant friction. Yet another object of the invention is to provide an electrical circuit breaker which is trip free, can be made for use with single phase or multiphase applications and which has fewer parts and less weight than prior art devices.
Briefly, an electrical circuit breaker made in accordance with the invention comprises a housing in which a stationary electrical contact and a movable contact mechanism having a movable electrical contact are mounted with the movable electrical contact being movable between contacts open and closed positions. The movable contact mechanism is pivotably mounted and is provided with a first spring member urging the movable contact mechanism toward the open contacts position. A push-button is mounted on the housing and is connected to one end of a plurality of end to end interjointed link members with the opposite end connected to the movable contact mechanism.
The first link is rotatably connected to the housing at a location intermediate to the first and second ends of the link. One end of the first link is formed with a slot to receive therethrough a pin of the push-button for converting linear motion of the push-button to rotary motion of the first link. The second end of the first link forms a first movable over center joint and is pivotably connected to the first end of a second link. The second end of the second link forms a second movable over center joint and is in turn pivotably jointed to the first end of a third link whose second end is pivotably connected to the movable contact mechanism. A stop surface is disposed on one side of, and closely adjacent to, a first imaginary straight line extending through the rotational connection of the first link to the housing and the second movable over center joint and a second imaginary straight line extending through the first movable over center joint and the pivotable connection of the second end of the third link.
A second spring member biases the second movable over center joint toward the stop surface and when the push-button is depressed the first link is rotated against the bias of the first spring member moving the movable contact mechanism toward the contacts closed position with the first movable over center joint moving over center across the first imaginary line and into engagement with the stop surface essentially straightening out the several links and moving the movable contact mechanism into the closed contacts position.
An overload responsive trip member in the form of a current carrying bimetal trip arm is caused to deflect upon a selected overload current which deflection is transferred to a rotatably mounted ambient bimetal compensator. Rotation of the bimetal compensator transfers motion through a motion transfer portion of the bimetal compensator to the second movable over center joint moving it over center to the other side of the second imaginary line thereby allowing the first spring member acting on the movable contact mechanism to open the contacts. As long as the overload bimetal member is in the overload deflected position the circuit breaker can not be reset even with the push-button held in the depressed position.
According to a feature of the invention, the second movable over center joint is provided with a roller engageable with the stop surface to avoid sliding motion. According to another feature, the movable contact mechanism is preferably formed to provide a preload to obtain a desired level of contact force as by bending a spring member into a generally J-shaped configuration, mounting the movable electrical contact on a stiffened distal free end of the long leg and forming a lost motion pin connection between an intermediate location of the long leg and the distal end portion of the short leg of the J-shaped configuration. The movable contact mechanism is pivotably mounted to the housing adjacent the bight portion between the two legs so that when the third link transfers motion to the contact mechanism and closes the contacts, the pin rides in the slot with the spring member supplying the contact force. According to yet another feature, multiphase circuit breakers made in accordance with the invention have adjacent phase mechanisms which include corresponding contact mechanisms, overload responsive members and motion transfer connecting plates along with an arm of the ambient bimetal compensator but do not include additional toggle mechanisms thereby resulting in a decreased part count and device weight.